Fix fOffset calculation with rule applying to the whole object.

If a read rule does not a specific target, the corresponding StreamerElement
has a name that is not one of the data member (past or present) and thus
they need to be handled explicitly in TBranchElement::InitializeOffset.
A new 'bit' (kWholeObject) is introduced to explicitly distinguish those
type of StreamerElement.
Optimized TStyle::AxisChoice()
Fixed 2 important bugs in TGeoXtru affecting DistFromOutside and ComputeNormal. Added outside flag in TGeoBranchArray. Added SetLastSafety in TGeoNavigator.
TDirectoryFile::GetKey() hash list optimization
export MACOSXVERS which is needed in the Makefile.macosx* included in conftest.mk.